The invention relates to a process for treating liquid electrolytes in electrochemical cells which are non-partitioned or partitioned by at least one separator and have at least one gas diffusion electrode.
The process is preferentially suitable for Faraday reactions or secondary reactions within the electrochemical cell which form gas and consume gas. However, the process is also suitable for electrochemical reactions in which no gases are involved.
It is known, particularly in reactions which consume gas, to use the gas diffusion electrode as a vertical vessel wall for the electrolyte and to supply, or to remove, the necessary gas to, or from, respectively, the rear side of the electrode. In order to assist the production from the electrolyte of any gas bubbles which are formed, the electrolyte flows upwards through the cell. The pressure difference between gas and electrolyte should really be the same at every point of the gas diffusion electrode. However, as a result of the difference in density between the gas and the liquid, a hydrostatic pressure which decreases as the height increases is set up. At great heights of construction such as are customary in industrial plants, it can therefore happen that, in the upper section, gas passes through the gas diffusion electrode into the electrolyte, while in the lower section electrolyte enters the gas space. Both effects interfere with the progress of the reaction and the operation of the plant.
In reactions in which gas is evolved, it is not absolutely necessary to keep the rear side of the gas diffusion electrode free from electrolyte. The gas diffusion electrodes can, therefore, dip vertically into the electrolyte, as known, for example, from expanded metal electrodes. The gas diffusion electrode can also be firmly attached to a separator. Gas bubbles which rise within the electrolyte are then formed on at least one side of the gas diffusion electrode. This two-phase flow causes pressure fluctuations and vibration. In addition, the electrodes and separators are subjected to varying loads along the height of construction as a result of the static pressure of the electrolyte. Although some effects can be moderated by low heights of construction and by enlarging the rearward electrolyte space behind the gas diffusion electrode, these effects cannot be eliminated.
French Patent Application 2,514,376 discloses an electrolysis process in electrolytic cells partitioned by separators, in which the electrolyte is passed as a film over the surface of an electrode under the influence of gravity. Any gas formed can escape through the openings in the expanded metal electrode located above. It is not mentioned how the process is to be carried out for industrial electrolysis processes which evolve or consume gas.